Current sensors measure the magnetic field surrounding a conductor of an electrical transmission system to monitor the current flowing through the conductor. Remote current sensors are positioned at a location sufficiently distant from the conductor to prevent electrical arcing from occurring without the use of an insulating material.
Electrical fault detectors have been known in which a Hall effect transducer is used to monitor the current flowing through a conductor, as shown in U.S. Pat. No. 4,539,520 issued to McBride on Sep. 3, 1985. A Hall effect transducer is positioned between a pair of tapered pole pieces having a wide cross-sectional area at one end and a small cross-sectional area at the opposite end, adjacent to the transducer. The tapered pole pieces concentrate low density magnetic flux in the air into a high density magnetic flux focused onto the transducer enabling the detection of a magnetic field from a distance which is greater than the electrical arcing distance. Typically, the sensor is positioned such that a flux-sensitive axis defined by the pole pieces is aligned tangentially with the magnetic field to achieve a sufficient concentration of magnetic flux on the transducer. The influence of the magnetic field is greatest when the axis of the sensor is tangential to the lines of magnetic flux and minimal when the axis perpendicular.
A problem arises with the prior art current sensing devices in applications wherein it is desired to independently monitor a number of electrical currents based on analysis of measurements taken in a composite magnetic field having components induced by each of currents. Because measurements of the composite magnetic field represent contributions of each of the currents, it is difficult to make an accurate determination of any one of the currents without knowing the relationship between the contributions. This problem is particularly troublesome in multi-phase power transmission systems.
In multi-phase electrical power systems, each of the different phases is transmitted by a different conductor, with the conductors of a typical three phase electrical transmission system being arranged in a parallel, triangular configuration. The current transmitted through each of the conductors induces a generally cylindrical magnetic field, which is superposed with the fields of the adjacent conductors. By aligning the sensitive axis of the current sensor tangential to the magnetic field associated with a particular current, so as to advantageously achieve the above noted necessary concentration of magnetic flux on the Hall effect transducer, the sensor necessarily is positioned so that it is influenced by the magnetic fields of the other two conductors. Accordingly, the measurement obtained by the current sensor is not indicative of only a single current but, rather, represents a composite of each of the currents.